This invention relates generally to the art of processing and treating molten metal. More particularly, this invention relates to a new and improved coupling design for a molten metal processing system.
Molten metal processing equipment can usually be classified into several different types of systems. For example, degassing/flux injection, submergence and pumps are frequently used general categories.
Systems which fall into the degassing/flux injection category generally operate to remove impurities from molten metal. More specifically, these systems remove oxides in solution, release dissolved gases, such as hydrogen, from molten metal, and through floatation to remove suspended solid impurities. In order to achieve these functions, gases or fluxes are introduced into a molten metal bath which chemically reacts with the impurities to convert them to a form (such as a precipitate or a dross) that can be separated readily from the remainder of the molten metal.
Systems which fall into the submergence category generally operate to melt scrap metal, such as by-products of metal processing operations and aluminum beverage cans, in order to recover the scrap metal for productive use. In a typical submergence system, the scrap metal is introduced onto the surface of the molten metal and drawn downward or submerged within the molten metal where it is melted. In its melted form, the scrap metal is substantially ready for productive use
The pump category can be further classified into three different types of systems including transfer pumps, discharge pumps, and gas-injection pumps. A transfer pump typically transfers molten metal from a furnace to a holding system or another furnace. A circulation pump transfers molten metal from one bath chamber to another bath chamber. A gas-injection pump circulates molten metal and adds a gas into the flow of molten metal. Although the present invention is particularly well suited for use with a gas-injection pump or degassing system, it must be appreciated that this invention may be used with any rotor/shaft system, including but not limited to the systems mentioned above.
Known molten metal processing apparatii of the foregoing types typically include the common feature of a motor carried by a motor mount, a shaft connected to the motor at an upper end, and an impeller or rotor connected at a lower end of the shaft. A coupling mechanism is used to connect the upper end of the shaft to the motor. The components are usually, but not limited to, manufactured from metals and/or refractory material, such as graphite or ceramic. In operation, the motor drives the coupling/shaft/rotor system about its central vertical axis. The rotating impeller may serve any number of functions. For example, in a submergence system the impeller may draw molten metal downwardly to assist in the submergence of scrap materials deposited on the surface of the melt. In a pump system, the impeller may be contained within a housing to effect a pumping action on the metal. In a degassing/flux injection system, the introduction of gas or flux into the molten metal is done via a passage located in the coupling/shaft/rotor system.
An important feature of impeller/shaft systems is the coupling mechanism which connects the upper end of the shaft to the motor. Typically, the coupling mechanism is made from a metal or other heat conductive material, for example stainless steel. Since the shaft/impeller system is typically immersed in a molten metal bath, the shaft temperature increases and thereby transfers heat to the coupling mechanism via conduction. Heat from the coupling mechanism can then be transferred to the output shaft of the motor. This heat can be detrimental to the performance of the motor.
Heat conduction is the transmission of heat across matter. Conduction is heat transfer by means of molecular agitation within a material without any motion of the material as a whole. If one end of a metal rod is at a higher temperature, then kinetic energy will be transferred down the rod toward the colder end because the higher speed particles will collide with the slower ones with a net transfer of energy to the slower ones. Heat transfer is always directed from a higher to a lower temperature. Dense substances typically are fair conductors; metals in general are good conductors. The law of heat conduction, also know as Fourier's law, states that the time rate of heat flow Q through a body is proportional to the gradient of temperature difference:
  Q  =      KA    ⁢                  ⁢                  Δ        ⁢                                  ⁢        T                    Δ        ⁢                                  ⁢        x            A is the transversal surface area, Δx is the thickness of the body of matter through which the heat is passing, K is a conductivity constant dependent on the nature of the material and its temperature, and ΔT is the temperature difference through which the heat is being transferred. This law forms the basis for the derivation of the heat equation.
Accordingly, a need exists in the art of processing molten metal to provide a coupling design for rotor/shaft systems which has a heat break to prevent heat flow to a motor. The present invention achieves such advantages and others. This disclosure deals with a cross sectional area reduction heat break which provides a restriction to prevent heat transmission through a conductive material.